24.3 Stereoisomerism in complex ions

• Stereoisomers have the same structural formulae but a different arrangement of the atoms in space
• Complex ions can display cis-trans isomerism and optical isomerism
• Cis and trans isomers exist in square planar complexes with

  • two molecules/ions of one monodentate ligand
  • two molecules/ions of another monodentate ligand
• In the cis isomer, the identical ligands are one the same side of the complex, next to each other
• In the trans isomer, the identical ligands are on opposite sides of the complex
• Cis-platin is used in chemotherapy as an anti-cancer drug
• Cis-platin works by forming a platinum complex which binds to DNA and prevents cell division
• Cis and trans isomers exist in octahedral complexes with

  • four molecules/ions of one monodentate ligand
  • two molecules/ions of another monodentate ligand
• In the cis isomer of octahedrals, the two identical monodentate ligands are next to each other
• In the trans isomer of octahedrals, the two identical monodentate ligands are opposite each other
• Optical isomerism only occurs in octahedral complexes containing two or three bidentate ligands
• Cis isomers of octahedral complexes have optical isomers if they have

  • two molecules/ions of a bidentate ligand
  • two molecules/ions of a monodentate ligand